Russian Chemical Bulletin, International Edition, Vol. 60, No. 12, pp. 2470—2484, December, 2011 2470 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2423—2436, December, 2011. 1066-5285/11/6012-2470 © 2011 Springer Science+Business Media, Inc. Molecular magnets based on chain polymer complexes of copper(II) bis(hexafluoroacetylacetonate) with isoxazolyl-substituted nitronyl nitroxides S. V. Fokin, S. E. Tolstikov, E. V. Tretyakov, G. V. Romanenko, A. S. Bogomyakov, S. L. Veber, R. Z. Sagdeev, and V. I. Ovcharenko International Tomography Center, Siberian Branch of the Russian Academy of Sciences, 3a ul. Institutskaya, 630090 Novosibirsk, Russian Federation. Fax: +7 (383) 333 1399. E-mail: Victor.Ovcharenko@tomo.nsc.ru First isoxazolyl-substituted nitronyl nitroxides (L and L Me 2 ) were synthesized and charac- terized. Their reactions with Cu(hfac) 2 and Mn(hfac) 2 (hfac is hexafluoroacetylacetonate) afford the heterospin complexes [Cu(hfac) 2 L] n , [Cu 2 (hfac) 4 L] n , [Cu 2 (hfac) 4 L Me 2 ] n , [Cu(hfac) 2 L Me 2 ] n , [Cu(hfac) 2 L Me 2 2 ], [Cu(hfac) 2 L Me 2 (MeCN)], [Mn(hfac) 2 ] 3 L 4 , and [Mn(hfac) 2 L Me 2 ] 2 . In the ligand L, the N atom of the isoxazole ring (N Iz ) has weak electron- donating properties. For example, the paramagnetic ligand in the chain polymer complex [Cu(hfac) 2 L] n acts as a bidentate bridging ligand coordinated through both O atoms of the nitronyl nitroxide group (O N—O ); the N Iz and O Iz atoms are not involved in the coordination. The introduction of Me groups into the isoxazole substituent results in an increase in the electron density on the N Iz atom and enables the synthesis of the chain polymer complex [Cu(hfac) 2 L Me 2 ] n , in which the bidentate bridging ligand L Me 2 is coordinated through the O N—O and N Iz atoms. In the mononuclear complexes [Cu(hfac) 2 L Me 2 2 ] and [Cu(hfac) 2 L Me 2 (MeCN)], the paramagnetic ligand is coordinated only through the N Iz atom. The solid heterospin Mn complexes [Mn(hfac) 2 ] 3 L 4 and [Mn(hfac) 2 L Me 2 ] 2 have a molecular structure. In these com- plexes, strong antiferromagnetic intracluster exchange interactions arise. The residual magnetic moments of the exchange clusters in the complex [Mn(hfac) 2 ] 3 L 4 are ferromagnetically cou- pled, resulting in the increase in the effective magnetic moment ( eff ) of the complex with decreasing temperature in the range of 300—30 K. The thermomagnetic study of the complexes [Cu(hfac) 2 L] n , [Cu 2 (hfac) 4 L] n , and [Cu 2 (hfac) 4 L Me 2 ] n in the range of 2—300 K revealed the ferromagnetic ordering at temperatures below 5 K. The ESR study of the solid complex [Cu(hfac) 2 L Me 2 ] n showed that the decrease in its  eff in the temperature range of 30—300 K is associated with the direct exchange interaction between the unpaired electrons of the nitronyl nitroxides of adjacent chains, whereas at temperatures below 30 K, only Cu 2+ ions contribute to the magnetic susceptibility of the complex. Key words: copper(II) complexes, manganese(II) complexes, coordination compounds, mag- nets, nitroxides, hexafluoroacetylacetonates, X-ray diffraction analysis, magnetic measure- ments. Magneto-structural relationships inherent in "breath- ing" crystals based on heterospin mixed-ligand coordina- tion compounds [Cu(hfac) 2 L Pz(R) ] n (hfac is hexafluoro- acetylacetonate, L Pz(R) is spin-labeled alkyl-substituted pyrazole) are extensively studied nowadays. Solid phases of these compounds are formed by polymer chains composed of alternating bis-chelate fragments and spin-labeled ligands. The characteristic feature of the crystals of [Cu(hfac) 2 L Pz(R) ] n is that they can undergo thermally induced structural rearrangements in the solid state accom- panied by magnetic anomalies, which are similar in char- acter to the temperature dependences of the effective mag- netic moment ( eff ) to the spin crossover phenomenon. 1—28 The investigation of the magnetic properties of the compounds [Cu(hfac) 2 L Pz(R) ] n showed that the variation of the alkyl substituent R in the ligand L Pz(R) has a sub- R = H, Me, Et, Pr, Pr i , Bu, CD 3 , C 2 D 5